Multi-step valve actuation system

ABSTRACT

A multi-step valve actuation system is provided to selectively open a poppet valve of an internal combustion engine having a camshaft rotatably supported by a cylinder block. The multi-step valve actuation system includes a rocker arm operable to selectively open the poppet valve and a pushrod operable to bias the rocker arm. A first follower arm is engageable with a first cam of the camshaft and operates to selectively bias the pushrod. A lash adjuster is disposed between the first follower arm and the pushrod. A second follower arm is engageable with a second cam of the camshaft and selectively latchable with respect to the first follower arm, while a third follower arm is engageable with a third cam of the camshaft and selectively latchable with respect to the first follower arm. An internal combustion engine incorporating the multi-step valve actuation system of the present invention is also disclosed.

TECHNICAL FIELD

The present invention relates to a multi-step valve actuation system foran internal combustion engine having an overhead valve,camshaft-in-block configuration.

BACKGROUND OF THE INVENTION

Recent advances in internal combustion engine operating strategies haveled to the development of two-step or multi-step valve actuationsystems. These systems allow two or more distinct valve lift profiles,thereby allowing a poppet valve of the internal combustion engine to beopened in accordance with one valve lift profile having a firstpredetermined maximum lift, when operating in one engine speed and loadcondition and to be opened in accordance with another valve lift profilehaving a second predetermined maximum lift, when operating in anotherengine speed and load condition. This two-step characteristic is usuallyfacilitated in overhead camshaft internal combustion engines through theuse of a switchable follower disposed between the camshaft, which isrotatably mounted with respect to a cylinder head, and the poppet valve.The increased amount of space required for the packaging of themulti-step valve actuation system has prevented its use within overheadvalve, camshaft-in-block internal combustion engines where space istypically limited.

SUMMARY OF THE INVENTION

A multi-step valve actuation system is provided to selectively open apoppet valve of an internal combustion engine having a camshaftrotatably supported by a cylinder block. The multi-step valve actuationsystem includes a pivotably mounted rocker arm operable to selectivelyopen the poppet valve and a pushrod operable to bias the rocker arm. Afirst follower arm is engageable with a first cam of the camshaft andoperable to selectively bias the pushrod. Similarly, a second followerarm is engageable with a second cam of the camshaft and is selectivelylatchable with respect to the first follower arm for unitary movement.The first and second cam have respective first and second maximum valvelifts, such that the second maximum valve lift is greater in magnitudethan the first maximum valve lift.

In operation, the poppet valve is opened to the first maximum valve liftwhen the second follower arm is unlatched from the first follower arm.Alternately, the poppet valve is opened to the second maximum valve liftwhen the second follower arm is latched to the first follower arm.

In one embodiment, a third follower arm is engageable with a third camof the camshaft and is selectively latchable with respect to the firstfollower arm for unitary movement. Additionally, the third cam has athird maximum valve lift of greater magnitude than the first and secondmaximum valve lifts. In operation, the poppet valve is opened to thethird maximum valve lift when the third follower arm is latched to thefirst follower arm.

A lash adjuster may be disposed between the first follower arm and thepushrod to account for clearances within the multi-step valve actuationsystem. The lash adjuster may be selectively collapsible to enabledeactivation of the poppet valve. Each of the first, second, and thirdfollower arms may rotatably support friction reducing roller assemblies.An internal combustion engine incorporating the multi-step valveactuation system is also disclosed.

The above features and advantages and other features and advantages ofthe present invention are readily apparent from the following detaileddescription of the best modes for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a portion of an internal combustionengine incorporating a multi-step valve actuation system of the presentinvention; and

FIG. 2 is a perspective view of a portion of the multi-step valveactuation system of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings wherein like reference numbers correspond tolike or similar components throughout the several figures, there isshown in FIG. 1 an internal combustion engine, generally indicated at10. The internal combustion engine 10 includes a cylinder block 12having a first bank of cylinders 14 and a second bank of cylinders 16. Afirst cylinder head 18, shown in phantom, and a second cylinder head 20are mounted to a respective one of the first and second bank ofcylinders 14 and 16. Only a portion of the first and second cylinderheads 18 and 20 are shown in FIG. 1. Those skilled in the art willrealize that in a complete internal combustion engine 10, the first andsecond cylinder heads 18 and 20 will span substantially the entirety ofthe respective first and second cylinder banks 14 and 16. The first andsecond bank of cylinders 14 and 16 are arranged in a generally V-shapedconfiguration, thereby defining a valley 22. Therefore, the internalcombustion engine 10 can be generally regarded as a V-type engine.

A selectively openable poppet valve 24 is at least partially containedwithin each of the first and second cylinder heads 18 and 20 and isoperable to allow the selective introduction of intake air into theinternal combustion engine 10. As such, the poppet valves 24 may beconsidered intake valves. Additionally, a selectively openable poppetvalve 26 is at least partially contained within each of the first andsecond cylinder heads 18 and 20 and is operable to allow the selectiveexhaust of products of combustion from the internal combustion engine10. As such, the poppet valves 26 may be considered exhaust valves. Thepoppet valves 24 and 26 are biased in a closed position by valve springs28 and 30, respectively. With the arrangement of the poppet valves 24and 26 discussed hereinabove, the internal combustion engine 10 may becharacterized as an overhead valve engine.

The internal combustion engine includes a multi-step valve actuationsystem 31. The multi-step valve actuation system 31 includes rocker arms32 and 34, pushrods 36 and 38, and camshaft 40. The camshaft 40 isrotatably supported within the cylinder block 12 by camshaft bearings42, shown in FIG. 2; therefore, the internal combustion engine 10 may befurther characterized as having a camshaft-in-block configuration. Therotation of the camshaft 40 forces or urges the pushrods 36 and 38 tobias the respective rocker arms 32 and 34 to effect the movement of therespective poppet valves 24 and 26 from the closed position to an openposition. The rocker arms 32 and 34 are pivotably mounted with respectto the first and second cylinder heads 18 and 20. The construction andoperation of the multi-step valve actuation system 31 will be discussedin greater detail with reference to FIG. 2. The hydraulic circuitryemployed for the operation of the multi-step valve actuation system 31has been removed from FIG. 1 for clarity.

Referring to FIG. 2, and with continued reference to FIG. 1, there isshown a portion of the multi-step valve actuation system 31 of FIG. 1further illustrating various aspects of the present invention. Thecamshaft 40 includes a plurality of cams 44 including first cams 46,second cams 48, and third cams 50 associated with the operation of thepoppet valves 24, i.e. the intake valves, of the internal combustionengine 10. Each of the first, second, and third cams 46, 48, and 50 havea predetermined valve lift profile with a predetermined maximum valvelift determined by the respective first, second, and third lobe portions52, 54, and 56. The first, second, and third cams 46, 48, and 50 furtherinclude respective first, second, and third base circle portions 58, 60,and 62. In the preferred embodiment, the predetermined maximum valvelift of the third cam 50 is greater than that of the second cam 48which, in turn, has a greater predetermined maximum valve lift than thatof the first cam 46.

Additionally, cams 64 are associated with the operation of the poppetvalves 26, i.e. the exhaust valves, of the internal combustion engine10. The cams 64 have a predetermined valve lift profile with apredetermined maximum valve lift determined by the lobe portion 66 ofeach of the cams 64, while a base circle portion 68 is also provided oneach of the cams 64.

First, second, and third follower arms 70, 72, and 74 are engageablewith the respective first, second, and third cams 46, 48, and 50. Eachof the first, second, and third follower arms 70, 72, and 74 rotatablysupports a roller assembly 76. The roller assemblies 76 operate toreduce the friction between the first, second, and third follower arms70, 72, and 74 and the respective first, second, and third cams 46, 48,and 50 during rotation of the camshaft 40. Those skilled in the art willrecognize that the roller assemblies 76 may be omitted, at the expenseof greater frictional losses, while remaining within the scope of thatwhich is claimed. The second and third follower arms 72 and 74 are eachdisposed on either side of the first follower arm 70 and are selectivelylatchable to the first follower arm 70 for unitary movement therewith.Those skilled in the art will recognize various methods of latching thesecond and third follower arms 72 and 74 with respect to the firstfollower arm 70, including, for example, a hydraulically actuated pin ora mechanically actuated pin. The latching of the second and thirdfollower arms 72 and 74 to the first follower arm 70 is preferablyperformed when the first, second, and third follower arm 70, 72, and 74are in contact with the base circle portions 58, 60, and 62 of therespective first, second, and third cams 46, 48, and 50.

Follower arms 78 are engageable with the cams 64 and include rollerassemblies 80, one of which is shown in FIG. 2, which are operable toreduce friction between the follower arms 78 and the cams 64 as thecamshaft 40 rotates. As with the roller assemblies 76, those skilled inthe art will recognize that the roller assemblies 80 may be omitted, atthe expense of greater frictional losses, while remaining within thescope of that which is claimed.

The follower arms 70, 72, 74, and 78 are pivotably mounted with respectto the cylinder block, shown in FIG. 1, by a shaft 82, shown with dashedlines in FIG. 2. The shaft 82 is spaced from the camshaft 40 and mountedsubstantially within the valley 22 of the internal combustion engine 10.By mounting the follower arms 70, 72, 74, and 78 within the valley 22 ofthe internal combustion engine 10, the multi-step valve actuation system31 may be efficiently packaged within a space that would otherwise havebeen left empty in traditional camshaft-in-block engine designs.Additionally, by packaging the follower arms 70, 72, 74, and 78 withinthe valley 22, the design changes required to the first and secondcylinder heads 18 and 20 to incorporate the multi-step valve actuationsystem 31 are minimized.

A hydraulic lash adjuster 84 is disposed between the first follower arm70 and the pushrod 36. Similarly, a hydraulic lash adjuster 86 isdisposed between the follower arm 78 and the pushrod 38. The hydrauliclash adjusters 84 and 86 are operable to account for the lash orclearance that may be present within the multi-step valve actuationsystem 31 during operation of the internal combustion engine 10.Preferably, each of the lash adjusters 84 and 86 each include a rollerassembly 88 operable to reduce friction within the multi-step valveactuation system 3 1. Additionally, the lash adjusters 84 and 86 may beselectively collapsible to allow the respective poppet valves 24 and 26to remain in the closed position irrespective of the rotation of thecamshaft 40. This type of operation is especially suited for so-calledActive Fuel Management or Displacement on Demand modes of engineoperation where at least one of the cylinders of the internal combustionengine 10 is deactivated by maintaining the poppet valves 24 and 26 inthe closed position. By maintaining the poppet valves 24 and 26 in theclosed position, the pumping losses of the internal combustion engine 10are decreased, thereby increasing operating efficiency. This mode ofoperation is beneficial during certain engine operating conditions, suchas low load engine operation.

A plunger 90 is biased by a spring 92 to urge the second follower armtoward the second cam 48. Similarly, a plunger 94 is biased by a spring96 to urge the third follower arm toward the third cam 50. The plungers90 and 94 and springs 92 and 96 cooperate to keep the respective secondand third follower arms 72 and 74 in contact with the respective secondand third cams 48 and 50 during modes of engine operation when thesecond follower arm 72 and/or third follower arm 74 are unlatched fromthe first follower arm 70.

The multi-step valve actuation system 31 of the present inventionprovides three valve lift profiles to the poppet valve 24. In operation,the internal combustion engine 10 may operate in a low lift mode ofoperation where the poppet valve 24 is selectively opened in accordancewith a predetermined valve lift profile having a predetermined maximumvalve lift. This mode of operation is accomplished by unlatching thesecond and third follower arms 72 and 74 from the first follower arm 70thereby allowing the first follower arm 70 to follow the profile of thefirst cam 46 and bias the pushrod 36 in accordance with the valve liftprofile of the first cam 46. The plungers 90 and 94 and springs 92 and96 cooperate to keep the respective second and third follower arms 72and 74 in contact with the respective second and third cam 48 and 50.Those skilled in the art will recognize that the first cam 46 may beformed such that it provides zero lift to the poppet valve 24 therebyallowing the deactivation of the associated cylinder of the internalcombustion engine 10.

When operating in the medium lift mode of operation, the second followerarm 72 is latched to the first follower arm 70 providing unitarymovement therewith. The second follower arm 72 will follow the valvelift profile of the second cam 48 and cause the first follower arm 70 tobias the pushrod 36 in accordance with that profile. The first followerarm 70 no longer follows the profile of the first cam 46 in the mediumlift mode of operation. The plunger 94 and spring 96 cooperate to keepthe third follower arm 74 in contact with the third cam 50.

When operating in the high lift mode of operation, the third followerarm 74 is latched to the first follower arm 70 providing unitarymovement therewith. The third follower arm 74 will follow the valve liftprofile of the third cam 50 and cause the first follower arm 70 to biasthe pushrod 36 in accordance with that profile. The first follower arm70 no longer follows the profile of the first cam 46 and in the highlift mode of operation. The plunger 90 and spring 92 cooperate to keepthe second follower arm 72 in contact with the second cam 48.Alternately, both the second and the third follower arm 72 and 74 may belatched to the first follower arm 70 during the high lift mode ofoperation.

Although the multiple lift functionality of the multi-step valveactuation system 31 has been described herein above with reference tothe selective opening of the poppet valves 24, i.e. the intake valves,those skilled in the art will recognize that the multiple liftfunctionality may be applied to the poppet valves 26, i.e. the exhaustvalves, should the operational strategies of the internal combustionengine 10 require such functionality. Additionally, a multi-step valveactuation system 31 having two lift functionality may be provided byeliminating the third follower arm 74 and the third cam 50. In thealternative, a multi-step valve actuation system 31 having greater thanthree distinct valve lifts may be provided by increasing the number offollower arms and respective cams.

The multi-step valve actuation system 31 may include a camshaft phaser,not shown, operable to adjust the timing of the camshaft 40, therebyproviding a greater range of valve actuation functionality. The internalcombustion engine 10 incorporating the multi-step valve actuation system31 of the present invention is especially suited for use with anelectrically variable hybrid transmission, or EVT, as the EVT may employthe variable valve lift and/or valve deactivation functionality providedby the multi-step valve actuation system 31 to optimize fuel economy.Further the multi-step valve actuation system 31 of the presentinvention may facilitate a Homogeneous Charge Compression Ignition, orHCCI, mode of operation for the internal combustion engine 10. Whenoperating in the HCCI mode of operation, the intake valve may requiremultiple valve lift strategies and possible valve deactivation.Additionally, by providing the exhaust valve with valve reopeningcapabilities, such as is possible with a two lobe cam, selectivere-breathing of products of combustion is possible thereby stabilizingthe HCCI combustion process.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims.

1. A multi-step valve actuation system to selectively open a poppetvalve of an internal combustion engine having a camshaft rotatablysupported by a cylinder block, the multi-step valve actuation systemcomprising: a rocker arm operable to selectively open the poppet valve;a pushrod operable to bias said rocker arm; a first follower armengageable with a first cam of the camshaft and operable to selectivelybias said pushrod; a second follower arm engageable with a second cam ofthe camshaft and selectively latchable with respect to said firstfollower arm for unitary movement; a third follower arm engageable witha third cam of the camshaft and selectively latchable with respect tosaid first follower arm for unitary movement; wherein said first andsecond cam have respective first and second maximum valve lifts, saidsecond maximum valve lift being greater in magnitude than said firstmaximum valve lift; wherein said third cam has a third maximum valvelift of greater magnitude than said first and second maximum valvelifts; wherein the poppet valve is opened to said third maximum valvelift when said third follower arm is latched to said first follower arm;wherein the poppet valve is opened to said first maximum valve lift whensaid second follower arm is unlatched from said first follower arm; andwherein the poppet valve is opened to said second maximum valve liftwhen said second follower arm is latched to said first follower arm. 2.(canceled)
 3. The multi-step valve actuation system of claim 1, furthercomprising a lash adjuster disposed between said first follower arm andsaid pushrod.
 4. The multi-step valve actuation system of claim 3,wherein said lash adjuster includes a roller assembly in contact withsaid first follower arm.
 5. The multi-step valve actuation system ofclaim 3, wherein said lash adjuster is selectively collapsible tomaintain the poppet valve in a closed position irrespective of camshaftrotation.
 6. The multi-step valve actuation system of claim 1, whereinat least one of said first and second follower arms rotatably supports aroller assembly engageable with a respective one of said first andsecond cams.
 7. The multi-step valve actuation system of claim 1,wherein said third follower arm rotatably supports a roller assemblyengageable with said third cam.
 8. The multi-step valve actuation systemof claim 1, wherein the internal combustion engine includes a cylinderhead mounted with respect to the cylinder block and wherein said rockerarm is pivotably mounted with respect to the cylinder head and thepoppet valve is at least partially contained within the cylinder head.9. The multi-step valve actuation system of claim 1, further comprisinga first spring member operable to bias said second follower arm towardsaid second cam.
 10. The multi-step valve actuation system of claim 9,further comprising a second spring member operable to bias said thirdfollower arm toward said third cam.
 11. An internal combustion enginecomprising: a cylinder block; a cylinder head mounted with respect tosaid cylinder block; a selectively openable poppet valve at leastpartially disposed within said cylinder head; a rocker arm pivotablymounted with respect to said cylinder head and operable to selectivelyopen said poppet valve; a camshaft having a plurality of cams androtatably supported within said cylinder block; a first follower armengageable with a first cam of said plurality of cams; a second followerarm engageable with a second cam of said plurality of cams andselectively latchable with respect to said first follower arm; a thirdfollower arm engageable with a third cam of said plurality of cams andselectively latchable with respect to one of said first and secondfollower arms; wherein said first and second cam have respective firstand second maximum valve lifts, said second maximum valve lift beinggreater in magnitude than said first maximum valve lift; wherein saidthird cam has a third maximum valve lift of greater magnitude than saidfirst and second maximum valve lifts; wherein said selectively openablepoppet valve is opened to said third maximum valve lift when said thirdfollower arm is latched to said one of said first and second followerarms; wherein said selectively openable poppet valve is opened to saidfirst maximum valve lift when said second follower arm is unlatched fromsaid first follower arm; and wherein said selectively openable poppetvalve is opened to said second maximum valve lift when said secondfollower arm is latched to said first follower arm.
 12. (canceled) 13.The internal combustion engine of claim 11, further comprising: a lashadjuster disposed between said first follower arm and said pushrod; andwherein said lash adjuster is one of a selectively collapsible andnon-collapsible type.
 14. The internal combustion engine of claim 13,wherein said lash adjuster includes a roller assembly in contact withsaid first follower arm.
 15. The internal combustion engine of claim 11,wherein at least one of said first and second follower arms rotatablysupports a roller assembly engageable with a respective one of saidfirst and second cams.
 16. The internal combustion engine of claim 11,wherein said third follower arm rotatably supports a roller assemblyengageable with said third cam.
 17. A multi-step valve actuation systemto selectively open a poppet valve of an internal combustion enginehaving a camshaft rotatably supported by a cylinder block, themulti-step valve actuation system comprising: a rocker arm operable toselectively open the poppet valve; a pushrod operable to bias saidrocker arm; a first follower arm engageable with a first cam of thecamshaft and operable to selectively bias said pushrod; a lash adjusterdisposed between said first follower arm and said pushrod; a secondfollower arm engageable with a second cam of the camshaft andselectively latchable with respect to said first follower arm; a thirdfollower arm engageable with a third cam of the camshaft and selectivelylatchable with respect to said first follower arm; wherein said first,second, and third cam have respective first, second, and third maximumvalve lifts; wherein said third maximum valve lift is greater inmagnitude than said second maximum valve lift and said second maximumvalve lift is greater in magnitude than said first maximum valve lift;wherein the poppet valve is opened to said first maximum valve lift whensaid second follower arm is unlatched from said first follower arm;wherein the poppet valve is opened to said second maximum valve liftwhen said second follower arm is latched to said first follower arm; andwherein the poppet valve is opened to said third maximum valve lift whensaid third follower arm is latched to said first follower arm.
 18. Themulti-step valve actuation system of claim 17, wherein said lashadjuster is selectively collapsible.
 19. The multi-step valve actuationsystem of claim 17, wherein at least one of said first, second, andthird follower arms include a roller assembly engageable with arespective one of said first, second, and third cams.
 20. The multi-stepvalve actuation system of claim 17, further comprising first and secondspring members operable to bias a respective one of said second andthird follower arms toward said respective second and third cams.